Evaluation of Amides, Carbamates, Sulfonamides, and Ureas of 4-Prop-2-ynylidenecycloalkylamine as Potent, Selective, and Bioavailable Negative Allosteric Modulators of Metabotropic Glutamate Receptor 5.

Negative allosteric modulators (NAMs) of the metabotropic glutamate receptor 5 (mGlu5) hold great promise for the treatment of a variety of central nervous system disorders. We have recently reported that prop-2-ynylidenecycloalkylamine derivatives are potent and selective NAMs of the mGlu5 receptor. In this work, we explored the amide, carbamate, sulfonamide, and urea derivatives of prop-2-ynylidenecycloalkylamine compounds with the aim of improving solubility and metabolic stability. In silico and experimental analyses were performed on the synthesized series of compounds to investigate structure-activity relationships. Compounds 12, 32, and 49 of the carbamate, urea, and amide classes, respectively, showed the most suitable cytochrome inhibition and metabolic stability profiles. Among them, compound 12 showed excellent selectivity, solubility, and stability profiles as well as suitable in vitro and in vivo pharmacokinetic properties. It was highly absorbed in rats and dogs and was active in anxiety, neuropathic pain, and lower urinary tract models.

Insights into the interaction of negative allosteric modulators with the metabotropic glutamate receptor 5: discovery and computational modeling of a new series of ligands with nanomolar affinity.

Metabotropic glutamate receptor 5 (mGlu5) is a biological target implicated in major neurological and psychiatric disorders. In the present study, we have investigated structural determinants of the interaction of negative allosteric modulators (NAMs) with the seven-transmembrane (7TM) domain of mGlu5. A homology model of the 7TM receptor domain built on the crystal structure of the mGlu1 template was obtained, and the binding modes of known NAMs, namely MPEP and fenobam, were investigated by docking and molecular dynamics simulations. The results were validated by comparison with mutagenesis data available in the literature for these two ligands, and subsequently corroborated by the recently described mGlu5 crystal structure. Moreover, a new series of NAMs was synthesized and tested, providing compounds with nanomolar affinity. Several structural modifications were sequentially introduced with the aim of identifying structural features important for receptor binding. The synthesized NAMs were docked in the validated homology model and binding modes were used to interpret and discuss structure-activity relationships within this new series of compounds. Finally, the models of the interaction of NAMs with mGlu5 were extended to include important non-aryl alkyne mGlu5 NAMs taken from the literature. Overall, the results provide useful insights into the molecular interaction of negative allosteric modulators with mGlu5 and may facilitate the design of new modulators for this class of receptors.

The approach of conformational chimeras to model the role of proline-containing helices on GPCR mobility: the fertile case of Cys-LTR1.

The homology modeling of GPCRs has benefitted vastly from the availability of some resolved structures, which allow the generation of many reliable GPCR models. However, the dynamic behavior of such receptors has been only minimally examined in silico, although several pieces of evidence have highlighted some conformational switches that can orchestrate the activation mechanism. Among such switches, Pro-containing helices play a key role in determining bending in TM helices and thereby the width of the TM bundle. The approach proposed herein involves the generation of a set of possible models (conformational chimeras) by exhaustively combining the two main conformations (straight and bent) that a Pro-containing helix can assume. This approach was validated by generating conformational chimeras for the Cys-LTR1 receptor, which is involved in contractile and inflammatory processes. The generated chimeras were then used for docking a small set of representative ligands. The results revealed the flexibility mechanisms of Cys-LTR1, showing how the docked agonists vary their stabilizing interactions, shifting from the open to closed state, and how the examined antagonists are able to block the receptor in an open and inactive conformation, thus behaving as inverse agonists. This study emphasizes the promising potential of chimera modeling, confirms the key role of proline residues in receptor activation, and suggests that docking results can be improved by considering the often-overlooked flexibility of receptors.